(1) Field of the Invention
The present invention relates to an apparatus for shearing a gob used in forming a funnel/panel of a cathode ray tube and, more particularly, to a shearing apparatus capable of obtaining a uniform sheared surface, an increased shearing speed, and loading a predetermined place of a mould with a gob.
(2) Description of the Prior Art
A molten glass article is pressed and cast in a mould installed under a shearing apparatus to obtain a panel/funnel of a cathode ray tube CRT. FIG. 3 shows, in a schematic view, a device for moulding the panel/funnel of the CRT. A melting container A transfers the molten glass article to a feeder B. The feeder B provides a predetermined amount of the molten glass article with the mould C. A shearing apparatus D between the feeder B and the mould C cuts the molten glass article to load the gob with the mould.
The shearing apparatus D is formed such that a pair of blades moves like scissors at the time of transferring the molten glass article thereto. Since the blade for cutting the molten glass article has a pneumatic cylinder as a driving force, the change of pneumatic pressure changes the speed of a scissors-like movement of the blade, which results in the gob having a nonuniform section.
After completing its stroke, the movement of the blade is temporarily stopped by force by a stopper, so that the movement speed is zero and then the blade returns to its open position. Such a forced stop results in vibrations of the blade at the very time of cutting to obtain the nonuniform section of the gob.
FIG. 4B is a graph illustrating a relation between a gob shearing time and a displacement when a conventional gob-shearing apparatus cuts the molten glass article. If a curved line is bisected, the left part shows the performance of cutting the molten glass article and the right part shows the resuming of the blade after completion of the cutting. The curved lines L1 and L2 indicates the movement of the left and right blades of the gob-shearing apparatus.
As shown in FIG. 4B, points of bends of the L1 and L2 do not agree with each other, which means a formation of the nonuniform section of the gob constitutes a principle factor of not loading the gob with the mould.
This type of shearing apparatus is described in U.S. Pat. No. 4,015,967.